Methods and apparatus for internet-scale routing using small-scale border routers

ABSTRACT

Methods and apparatus for Internet-scale routing using small-scale border routers and IP tunneling are described. Each border router is directly connected to a transit provider. Routing protocol peerings may be passed via the border routers through tunnels to a routing service; the routing service and the transit provider router(s) appear to be directly adjacent routing peers. The routing service receives routing data from the transit provider(s), maintains the routing data in a routing table, and processes the routing data in the routing table to select best paths. A mapping service may be informed, by the routing service, of a best exit point (or points) for each Internet prefix of each packet to be routed on the Internet. Outbound packets from devices on the network to the Internet, and inbound packets from the Internet to the network devices, may be encapsulated and passed through tunnels as directed by the mapping service.

BACKGROUND Network/Internet Routing

The Internet, sometimes called simply “the Net,” is a worldwide systemof computer networks in which any one computer on a network may, withproper permission, obtain information from, or send information to, anyother computer on any other network on the Internet. Routing may bedefined as the process of selecting paths, or routes, on a network alongwhich to send network traffic. In computer networks, including theInternet, routing technologies direct the transit of data from a sourceto a destination through various intermediate devices (which may becollectively referred to as routers). A key routing technology for theInternet is the routing protocol. Currently, the routing protocol usedon the Internet is Border Gateway Protocol (BGP), defined originally inNetwork Working Group Request for Comments (RFC) 1771 and updated in RFC4271. RFC 4271 defines BGP as an inter-Autonomous System (AS) routingprotocol. BGP-enabled systems or devices on a network exchange networkreachability (routing) information with other BGP systems or devices onthe network. When a BGP-enabled system establishes a BGP connection toanother system on a network, the systems interchange BGP messages toupdate Internet routing information on the systems. The collection ofrouting information on a BGP system is generally referred to as arouting table. BGP may be used for routing data internally on networksand for routing data external to networks (e.g., from one network toanother on the global Internet). BGP used internally on networks may bereferred to as internal BGP (iBGP); external (Internet) BGP may bereferred to as eBGP.

On the global Internet, connectivity between networks may be provided bytransit providers. (However, networks may also establish peerconnections). Transit providers may be defined as generally largenetworks expressly for the purpose of providing connectivity for theInternet. A transit provider network is sometimes referred to as a“backbone.” Transit providers may be, but are not necessarily,commercial enterprises that charge for routing packets via their networkinfrastructure. Transit providers may provide local, regional, orinternational/global routing on the Internet. Examples of transitproviders include, but are not limited to, Verizon® and Level 3®Communications.

Generally, to use a transit provider, a network must have at least onephysical connection, e.g. a fiber optic or cable connection, to at leastone transit provider edge or border router, via which routing protocolinformation, and data packets, may be exchanged. While a network mayconnect to a single transit provider to establish a presence on theInternet via the transit provider, many networks, especially largernetworks (e.g., carriers, content delivery networks (CDNs), and largeenterprises), may establish and maintain such connections to multipletransit providers. FIG. 1A illustrates several networks 120A through120F each physically connected to two transit providers 110A and 110B.The device(s) on a network 120 that are physically connected to transitprovider border routers may generally be referred to as border routers.Networks 120 may include a range of networks from small networks, suchas local networks for small businesses, schools, government entities, orother relatively small public or private enterprises, to large networks,such as networks for large businesses, schools, government entities, orother relatively large public or private enterprises. Networks 120 mayalso include local or regional Internet Service Providers (ISP) thatprovides Internet connectivity to residential customers, small entities,etc. Networks 120 may also include the networks of commercial Webenterprises or e-businesses that, for example, provide electronic retailsales or web services to customers via the Internet. A network 120 mayinclude two or more subnetworks, data centers, smaller local networks,or other network components that are interconnected to form a largernetwork 120.

FIG. 1B illustrates example routes between two networks provided by twotransit providers. Border routers of networks 120A and 120B arephysically connected to border routers of transit providers 110A and110B. Each transit provider 110 may provide one or more paths or routesbetween networks 120A and 120B via which packets may be sent. Each routepasses through one or more nodes of the respective transit provider 110.A node may be a switch, router, computer system, or any other networkingcomponent. A path may pass through one or more external nodes as shownon route 110A1. An external node may, for example, be a border router ofanother network. Each route may include one or more “hops,” theconnection between two nodes via which packets are exchanged. As shownin FIG. 1B, some routes may have fewer hops than other routes. Forexample, route 110A3 includes two hops (ignoring the physicalconnections between the border routers), while route 110B2 includes fourhops. Each transit provider 110 provides routing information to eachconnected network 120 via routing protocol (e.g., BGP) sessionsestablished between the border routers. This routing informationincludes descriptions of the routes provided by the respective transitprovider 110 between the networks 120A and 120B, as well as thedescriptions of routes to other networks 120.

Conventionally, the border router and transit provider router establisha routing protocol (e.g., BGP) connection over the physical connection,and the transit provider router provides the border router with routinginformation available through the transit provider. The border routercollects and stores this routing information (and routing informationfrom other transit providers, if any, that the border router isconnected to) as a routing table. The routing table for the globalInternet may be referred to as the global Internet routing table. Thenetwork border router may perform other functions on the routinginformation, for example assuring that there are no “loop” routes in therouting table by excluding routes that include the network's borderrouter.

The global Internet routing table is large, currently including over300,000 routes, and is growing steadily. Many networks, for examplecarriers, content delivery networks (CDNs), and large enterprisenetworks, may need to route their external traffic based on the entireInternet routing table. Larger networks are generally connected to twoor more transit providers and peers, and must choose appropriate routesto different parts of the Internet. Most other types of routing(enterprise and much of what happens internally within data centers ornetworks) may require much smaller routing tables (1000s of routes);Internet-bound traffic is handed off to transit providers for routing.Generally, high speed routing (10 gb and up) is hardware accelerated:custom ASICs (Application-Specific Integrated Circuits) perform the bulkof the work, with traditional CPUs (Central Processing Units) performingcontrol-plane functions. A key feature of these ASICs is the size of theforwarding table or Forwarding Information Base (FIB) that they support.Larger FIBs substantially increase the cost and complexity of the ASICs.

A result of the above is that the route table capacity of networkingdevices has become bi-modal in distribution between Internet-scalerouters and commodity routers. Internet-scale routers (referred toherein as large-scale routers) may support one million or more routes.These large-scale routers are manufactured by a relatively small numberof companies (e.g., Cisco® Systems, Inc. and Juniper® Networks, Inc.),tend to be expensive (e.g., $300,000-$1,000,000), and sell in relativelysmall volumes. In addition, these systems are generally proprietarysystems that typically do not support customization or user extension.Commodity routers (referred to herein as small-scale routers) support amuch smaller number of routes (e.g., 16K-32K routes), and high marketvolume tends to keep prices relatively low (e.g., $15,000 and under).Most networks use these small-scale routers for internal network routing(e.g., using Open Shortest Path First (OSPF)), although some very largenetworks may use large-scale routers for at least some internalnetworking.

FIG. 1C illustrates a network connected to the Internet via physicalconnections between transit providers and large-scale border router(s),according to the prior art. Network 120A may include multiple computingand peripheral devices 150 such as servers, workstations, printers,storage systems, etc., which may be referred to as endpoint devices, aswell as multiple internal networking devices 140 such as internal(generally small-scale) routers, switches, bridges, etc. Network 120Amay need to route inbound and outbound external traffic to othernetworks or devices on the Internet based on the entire Internet routingtable 132. Conventionally, because of the large number of routes in theglobal Internet routing table (300,000+), network 120 will include oneor more large-scale border routers 130 that are each physicallyconnected to one or more transit provider 110 border routers, that eachestablish BGP sessions with connected transit providers 110, and thatare each configured to store the full Internet routing table 132.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates an example of networks each connected to two transitproviders.

FIG. 1B illustrates an example of routes between two networks providedby two transit providers.

FIG. 1C illustrates an example network connected to the Internet viaphysical connections between transit providers and large-scale borderrouter(s).

FIG. 2 illustrates an example network with full Internet access usingsmall-scale, commodity routers, according to at least some embodiments.

FIG. 3 illustrates establishing a routing protocol peering between atransit provider and a routing service, according to at least someembodiments.

FIG. 4 illustrates a method for routing a packet from a network deviceonto the Internet, according to some embodiments.

FIG. 5 illustrates a method for routing a packet received from theInternet to a target device on a network, according to some embodiments.

FIG. 6 illustrates an example network that implements hardwarevirtualization technology and that provides full Internet access usingsmall-scale, commodity routers, according to at least some embodiments.

FIG. 7 illustrates a method for routing a packet from a virtual machine(VM) on a network implementing hardware virtualization technology ontothe Internet, according to some embodiments.

FIG. 8 illustrates a method for routing a packet received from theInternet to a target VM on a network implementing hardwarevirtualization technology, according to some embodiments.

FIG. 9 illustrates establishing a routing protocol peering between atransit provider and a routing service using a TCP proxy, according toat least some embodiments.

FIG. 10 is a block diagram illustrating an example computer system thatmay be used in some embodiments.

While embodiments are described herein by way of example for severalembodiments and illustrative drawings, those skilled in the art willrecognize that embodiments are not limited to the embodiments ordrawings described. It should be understood, that the drawings anddetailed description thereto are not intended to limit embodiments tothe particular form disclosed, but on the contrary, the intention is tocover all modifications, equivalents and alternatives falling within thespirit and scope as defined by the appended claims. The headings usedherein are for organizational purposes only and are not meant to be usedto limit the scope of the description or the claims. As used throughoutthis application, the word “may” is used in a permissive sense (i.e.,meaning having the potential to), rather than the mandatory sense (i.e.,meaning must). Similarly, the words “include,” “including,” and“includes” mean including, but not limited to.

DETAILED DESCRIPTION OF EMBODIMENTS

Various embodiments of methods and apparatus for achievingInternet-scale routing using small route table commodity devices (i.e.,small-scale routers) and Internet Protocol (IP) tunneling are described.Conventionally, because of the large number of routes in the globalInternet routing table, a network wishing to perform Internet-scalerouting would include one or more large-scale border routers eachphysically connected to one or more transit providers and each capableof storing the entire global Internet routing table. Embodiments mayprovide a combined hardware and software solution that enables theconfiguration of very high capacity networks with full Internet accessusing small-scale, commodity routers that are not capable of storing theentire Internet routing table as border routers, rather than large-scalerouters as is conventionally required to support full Internet accessusing the entire Internet routing table. In addition to the small-scalerouters used as border routers, at least some embodiments may employ anInternet Protocol (IP) tunneling technology to provide the overlaynetwork, a routing service technology, and a mapping service technology.Each of these technologies is further described below in reference toFIG. 2.

Using these technologies and small-scale routers as border routers,embodiments enable the routing of traffic to and from the Internetwithout a large-scale router in the traffic path that is capable ofholding the entire Internet routing table. This allows a network to beconfigured to support Internet-scale routing at less cost thanconventional systems employing large-scale routers as border routers.The use of small-scale routers as border routers may also addflexibility to routing, as a network employing small-scale borderrouters, routing service technology, and mapping service technology maybe more easily configurable to support the application of otherparameters, such as business logic and network weather parameters, inrouting decisions than are conventional networks employing large-scalerouters as border routers.

FIG. 2 illustrates an example network with full Internet access usingsmall-scale commodity routers, according to at least some embodiments.Internet transit providers 210 use a routing protocol (e.g., theexternal Border Gateway Protocol (eBGP)) to communicate with customers(e.g., network 220) and pass routing information to and fro.Conventionally, eBGP requires that an eBGP peering is established withan adjacent and directly connected peer, e.g. a directly connectedborder router such as large-scale border router 130 of FIG. 1C. Therouting protocol session, once established (e.g., an eBGP session) thencommunicates routing information directly between the transit providerrouter and the directly connected border router (e.g., large-scaleborder router 130 of FIG. 1C). Referring again to FIG. 2, instead ofusing large-scale border routers, one or more small-scale border routers230 may be directly connected to the transit provider 210 router(s). Thesmall-scale border routers 230 may be commodity routers that support asmaller number of routes (e.g., 16K-32K routes) than do large-scalerouters; market volume tends to keep prices of these small-scale routersrelatively low (e.g., $15,000 and under) when compared to large-scalerouters. In addition, small-scale routers are generally more flexiblethan large-scale routers, and are generally easier to program andconfigure for custom applications and custom routing preferences andparameters. Network devices that may be used in the small-scale borderrouter space to implement the small-scale border routers may include,but are not limited to, general purpose servers, for example runningLinux technology.

In some embodiments, each small-scale border router 230 is directlyconnected (e.g., via a fiber optic or cable connection) to one and onlyone transit provider 210. In some embodiments, the routing protocolpeerings (e.g., eBGP peerings) are passed via the small-scale borderrouters 230 through transparent tunnels (provided via an overlaynetwork, implemented according to an IP tunneling technology, on network220) to a routing service 260 so that the routing service 260 and thetransit provider 210 router(s) appear to be directly adjacent at Layer 2of the network. In other embodiments, other methods may be used toestablish the routing protocol peerings between the transit provider 210router(s) and the routing service 260. For example, in some embodiments,a Transmission Control Protocol (TCP) pass-through proxy may beimplemented on each border router 230. The TCP proxies passes throughthe routing protocol peerings via connections to the routing service 260at the application layer of the network. Using these methods toestablish routing protocol peerings between transit provider 210router(s) and routing service 260, to routing protocol (e.g., eBGP)sessions on transit provider(s) 210, it appears as if the routingservice 260 is an adjacent peer and a border router; the transitprovider(s) 210 may not even be aware that the routing protocol peeringshave been “tunneled” or passed through to the routing service 260.

Note that, in some embodiments, a border router 230 may be connected tomore than one transit provider router or to more than one transitprovider 210, with appropriate logic on the border router 230 to supportdecision making for the multiple exit paths to the Internet. Also, insome embodiments, more than one border router 230 may be connected to agiven transit provider 210.

Routing Service

In at least some embodiments, the routing service 260 may be a softwarecontrol system that may be implemented, for example, on one or moreserver systems, which may be standard commodity servers. However, insome embodiments, for example for smaller deployments, the routingservice 260 may be implemented and executed in part or in full on otherdevices on the network than on dedicated server systems. For example, aswell as serving as border routers, typical network devices that may beused in the small-scale border router space may also be general purposeservers, for example running Linux technology, on which other processesmay be implemented. Thus, in some embodiments, the routing service 260may be implemented at least in part on the border router(s) 230. In atleast some embodiments, only routing information flows through therouting service 260 server(s); actual data traffic (data packets beingsent from endpoint devices 250 to Internet destinations and data packetsbeing received by endpoint devices 250 from Internet sources) does nottraverse the routing service 260 server(s). Routing service 260 receivesall upstream routing data from the Internet transit provider(s) 210,maintains the routing data in an Internet routing table 262, processesthe routing data in routing table 262 to select best paths for eachInternet prefix, and distributes the processed routing data to a mappingservice 270.

In at least some embodiments, routing service 260 serves as theauthoritative router for the network 220. As the authoritative routerfor the network, routing service 260 directs the routing of outgoingpackets from endpoint devices 250 on the network 220 onto the Internetvia the one or more network border routers 230 according to the routinginformation in the Internet routing table 262, and directs the routingof incoming packets from the Internet to endpoint devices 250 on thenetwork 220. The network border routers 230 do not store the fullInternet routing table, and do not direct the routing of packets to andfrom the Internet. Instead, to route packets, the network border routers230 query the routing service 260 for routing information.

However, in some embodiments, the network border routers 230 maymaintain a local cache of some routing information (but not the entireInternet routing table), for example routing information for hightraffic routes and/or important routes such as a default route foroutbound traffic. In these embodiments, when a network border router 230receives a packet to be routed, the network border router 230 may firstcheck the local cache to see if there is cached routing information forthe packet. If there is cached routing information for the packet in thelocal cache, the network border router 230 may route the packetaccording to the cached routing information. If there is no cachedrouting information for the packet in the local cache, the networkborder router may query routing service 260 (or query mapping service270, which obtains routing information from routing service 260) toobtain routing information for the packet, and route the packetaccording to the obtained routing information. The network border router230 may, but does not necessarily, cache the obtained routinginformation in the local cache.

FIG. 3 illustrates establishing a routing protocol peering between atransit provider and a routing service, according to at least someembodiments. As indicated at 300, a routing protocol (e.g., BGP) sessionis established between a small-scale border router 230 and a transitprovider 210 router. BGP (Border Gateway Protocol) is implemented on topof TCP (Transmission Control Protocol); to establish a BGP session, aTCP connection is first established between the border router 230 andthe transit provider 210 router. As indicated at 302, routing messagesare sent from the transit provider 210 to the border router 230 via therouting protocol session. As indicated at 304, the border routerencapsulates the routing messages and sends the encapsulated messages tothe routing service 260 via a tunnel on an overlay network implementedaccording to an IP tunneling technology. As indicated at 306, therouting service 260 strips the encapsulation from the routing messagesand processes the routing information in the routing messages. At leastsome of the routing information is stored to Internet routing table 262.

Mapping Service

The mapping service 270 may be informed, by the routing service 260, ofa best exit point (or points) for each Internet prefix of each packet tobe routed on the Internet. In addition, the mapping service 270 may beconfigured to perform some functionality of the IP tunneling technologyas described herein. Mapping service 270 may be aware of all network 220IP prefixes and the IP addresses of routers or other devices serving IPaddresses. Thus, various entities on the network 220 may query themapping service 270 to obtain internal network 220 address informationand/or Internet routing exit points. The mapping service 270 may becentralized, for example on a server system, or alternatively may bedistributed on two or more server systems or other devices. For example,in some embodiments, the mapping service 270 may be implemented at leastin part on the border router(s) 230. In at least some embodiments,actual data traffic does not traverse the mapping service 270 server(s).

The routing service 260 and the mapping service 270 may be implementedon separate devices or systems, or alternatively may both be implementedon the same device(s) or system(s). Furthermore, while FIG. 2 shows therouting service 260 and the mapping service 270 as separate elements, insome embodiments these two services may be merged into one service.

Routing Outbound Packets

FIG. 4 illustrates a method for routing a packet from a network deviceonto the Internet, according to some embodiments. In at least someembodiments, when a device 250 has a packet to send to an IP address,the device 250 queries the mapping service 270 to determine where toforward the packet, as indicated at 400. If this packet is destined forthe Internet, the mapping service 270 obtains a best exit point for theInternet prefix indicated by the packet from the routing service 260, asindicated at 402. The mapping service 270 returns the IP address of therelevant border router 230 serving the best exit point to the device250, as indicated at 404. The device 250 encapsulates the originalpacket in an IP tunneling encapsulation format and forwards theencapsulated packet across the network to the correct exit point (therelevant border router 230) via a tunnel 282, as indicated at 406. Theborder router 230 serving the exit point strips off the IP tunnelingencapsulation to reveal the original packet and forwards the packet tothe appropriate transit provider 210, as indicated at 408. The transitprovider 210 routes the packet as normal to the indicated Internet IPaddress.

While the above describes the device 250 as querying the mapping service270 to determine where to forward a packet when the device 250 has apacket to send to an IP address, it is not generally feasible to querythe mapping service for every packet or even every flow. Thus, in atleast some embodiments, devices such as device 250 may maintain a localcache of routing information. In some embodiments, the local cache maybe pre-populated for some routes, for example for high traffic routesand/or important routes. The device 250 may first check the local cacheto determine if there is cached routing information for the IP address.If the routing information is not in the local cache, then the device250 may query the mapping service.

In some embodiments, instead of the device 250 querying the mappingservice and encapsulating the packet, a router or other device 240 mayreceive the packet from device 250 and similarly query the mappingservice, perform the encapsulation, and forward the packet to therelevant border router 230.

Routing Inbound Packets

FIG. 5 illustrates a method for routing a packet, received from theInternet, to a target device on a network, according to someembodiments. As indicated at 500, a small-scale border router 230receives a packet from a transit provider 210. As indicated at 502, theborder router 230 queries the mapping service 270 with a destination IPaddress on the network. Mapping service 270 is aware of all network 220IP prefixes and the IP addresses of the router or other device servingthe destination IP address. As indicated at 504, the mapping service 270returns the IP address of the router or other device serving thedestination IP address to the border router 230. As indicated at 506,the border router 230 encapsulates the original packet in an IPtunneling encapsulation format and forwards the encapsulated packetacross the network via a tunnel 282 to the router or other deviceserving the destination IP address. As indicated at 508, the router orother device serving the IP address strips off the IP tunnelingencapsulation and forwards the original packet to the destination IPaddress.

While the above describes the border router 230 as querying the mappingservice 270 to determine where to forward a packet when the borderrouter 230 has a packet to send to a destination IP address on thenetwork, it is not generally feasible to query the mapping service forevery packet or even every flow. Thus, in at least some embodiments,border router 230 may maintain a local cache of routing information. Insome embodiments, the local cache on a border router 230 may bepre-populated for some routes, for example for high traffic routesand/or important routes. The border router 230 may first check the localcache to determine if there is cached routing information for an IPaddress. If the routing information is not in the local cache, then theborder router 230 may query the mapping service.

IP Tunneling Technology

As mentioned above, at least some embodiments may employ an InternetProtocol (IP) tunneling technology to provide an overlay network viawhich routing protocol peerings between the transit providers 210 andthe routing service 260 are established, and via which encapsulatedpackets may be passed through an IP tunneling substrate 280 usingtunnels 282. The IP tunneling technology may provide a mapping andencapsulating system for creating an overlay network on a network (e.g.,network 220 of FIG. 2) and may provide a separate namespace for theoverlay layer and the substrate 280 layer. Packets in the overlay layermay be checked against a mapping directory (e.g., provided by mappingservice 270) to determine what their tunnel substrate target should be.The IP tunneling technology provides a virtual network topology; theinterfaces that are presented to “customers” are attached to the overlaynetwork so that when a customer provides an IP address that they want tosend packets to, the IP address is run in virtual space by communicatingwith a mapping service (e.g., mapping service 270) that knows where theIP overlay addresses are.

In at least some embodiments, the IP tunneling technology may map IPoverlay addresses to substrate IP addresses, encapsulate the packets ina tunnel between the two namespaces, and deliver the packet to thecorrect endpoint via the tunnel, where the encapsulation is strippedfrom the packet. In some embodiments, the packet may be encapsulated inan IP tunneling packet format before sending, and the IP tunnelingpacket may be stripped after receiving. In other embodiments, instead ofencapsulating packets in IP tunneling packets, an IP tunneling addressmay be embedded in a substrate address of a packet before sending, andstripped from the packet address upon receiving. As an example, theoverlay network may be implemented using 32-bit IPv4 (Internet Protocolversion 4) addresses, and the IPv4 addresses may be embedded as part of128-bit IPv6 (Internet Protocol version 6) addresses used on thesubstrate network.

Example embodiments of an IP tunneling technology that may be used in atleast some embodiments are described in U.S. patent application Ser. No.12/060,074, titled “CONFIGURING COMMUNICATIONS BETWEEN COMPUTING NODES,”filed Mar. 31, 2008, whose inventor is Daniel T. Cohn, and which ishereby incorporated by reference in its entirety.

Networks with Hardware Virtualization

Some networks in which embodiments may be implemented may includehardware virtualization technology that enables multiple operatingsystems to run concurrently on a host computer, i.e. as virtual machines(VMs) on the host. The VMs may, for example, be rented or leased tocustomers of the network provider. A hypervisor, or virtual machinemonitor (VMM), on a host presents the VMs on the host with a virtualplatform and monitors the execution of the VMs. Each VM may be providedwith one or more IP addresses; the VMM on a host may be aware of the IPaddresses of the VMs on the host. As previously mentioned, mappingservice 270 may be aware of all network 220 IP prefixes and the IPaddresses of routers or other devices serving IP addresses. Thisincludes the IP addresses of the VMMs serving multiple VMs. A networkmay be configured to use the mapping service technology and IP tunnelingtechnology described herein to, for example, route data packets betweenVMs on different hosts within the network. In addition, a network may beconfigured to use the mapping service technology, IP tunnelingtechnology, and routing service technology described herein to routepackets from the VMs to Internet destinations, and from Internet sourcesto the VMs.

FIG. 6 illustrates an example network that implements hardwarevirtualization technology and that provides full Internet access usingsmall-scale, commodity routers, according to at least some embodiments.The network 620 may implement IP tunneling technology, mapping servicetechnology, and routing service technology as described herein to routepackets from the VMs 694 on hosts 690 to Internet destinations, and fromInternet sources to the VMs 694.

Routing Outbound Packets from a VM

In at least some embodiments, when a VM 694 sends a packet on thenetwork 620, the VMM 692 on the host 690 intercepts the packet. The VMM692 queries the mapping service 670 to determine where to forward thepacket. If the packet is destined for the Internet, the mapping service670 returns the IP address of the relevant border router 630 serving thebest exit point. The VMM 692 encapsulates the original packet in the IPtunneling encapsulation format and forwards the packet across thenetwork 620 to the correct exit point. The border router 630 serving theexit point strips off the IP tunneling encapsulation to reveal theoriginal packet, and forwards the packet to the transit provider 610,which routes it as normal to the Internet IP address.

FIG. 7 illustrates a method for routing a packet from a VM on a networkimplementing hardware virtualization technology onto the Internet,according to some embodiments. Each VM 694 may have a public internet IPaddress. It is to be noted that there may be some VMs that do not havepublic IP addresses. Additionally, there may be other classes of devicesthat have public IP addresses, such as virtual firewalls and loadbalancers. As indicated at 700, a VM 694 on a host 690 sends a packet toa public destination internet IP address. As indicated at 702, thepacket is intercepted by the VMM 692 on the host 690. As indicated at704, the VMM 692 queries the mapping service 670 with the IP address ofthe destination. As indicated at 706, the mapping service 670 isinformed of all internet prefixes and the IP address(es) of the bestexit point(s) for the packet by the routing service 660. As indicated at708, the mapping service 670 returns the IP address of the best exitpoint(s) to the VMM 692. As indicated at 710, the VMM 692 encapsulatesthe original packet in an IP tunneling encapsulation format and forwardsthe encapsulated packet across the network 620 to the correct exit pointvia a tunnel 682. For example, the VMM 692 may forward the packet to thenext-hop router. The next-hop router sees the packet as having thesource address of the VMM 692 and a destination address of the borderrouter 630 serving the selected exit point. The network 620 transportsthe packet to the border router 630 serving the selected exit point viathe tunnel 682. As indicated at 712, the border router 630 serving theselected exit point strips off the outer IP tunneling encapsulation andreveals the original packet with the public source and destination IPaddresses, and forwards the packet to the transit provider 610. Thetransit provider 610 sees an ordinary internet IP packet and forwardsthe packet accordingly.

In some embodiments, instead of the VMM 692 querying the mapping serviceand encapsulating the packet, a router or other device 640 may receivethe packet from VMM 692 and similarly query the mapping service, performthe encapsulation, and forward the packet to the relevant border router630.

While the above describes the VMM 692 as querying the mapping service670 to determine where to forward a packet when the VMM 692 intercepts apacket to send to an IP address, it is not generally feasible to querythe mapping service for every packet or even every flow. Thus, in atleast some embodiments, a VMM 692 may maintain a local cache of routinginformation. In some embodiments, the local cache may be pre-populatedfor some routes, for example for high traffic routes and/or importantroutes. The VMM 692 may first check the local cache to determine ifthere is cached routing information for the IP address. If the routinginformation is not in the local cache, then the VMM 692 may query themapping service.

Routing Inbound Packets to a VM

FIG. 8 illustrates a method for routing a packet received from theInternet to a target VM on a network implementing hardwarevirtualization technology, according to some embodiments. As indicatedat 800, a small-scale border router 630 receives a packet from a transitprovider 610. As indicated at 802, the border router 630 queries themapping service 670 with a destination IP address on the network.Mapping service 670 is aware of all network 620 IP prefixes and the IPaddresses of the router or other device serving the destination IPaddress. As indicated at 804, the mapping service 670 returns the IPaddress of the VMM 692 serving the destination IP address to the borderrouter 630. As indicated at 806, the border router 630 (or, in someembodiments, some other device, such as a top-of-rack router)encapsulates the original packet in an IP tunneling encapsulation formatand forwards the encapsulated packet across the network via a tunnel 682to the VMM 692 serving the destination IP address. As indicated at 808,the VMM 692 serving the IP address (or, alternatively, a router servingthe VM 694) strips off the IP tunneling encapsulation and forwards theoriginal packet to the VM 694 with the destination IP address.

While the above describes the border router 630 as querying the mappingservice 670 to determine where to forward a packet when the borderrouter 630 has a packet to send to a destination IP address on thenetwork, it is not generally feasible to query the mapping service forevery packet or even every flow. Thus, in at least some embodiments,border router 630 may maintain a local cache of routing information. Insome embodiments, the local cache on a border router 630 may bepre-populated for some routes, for example for high traffic routesand/or important routes. The border router 630 may first check the localcache to determine if there is cached routing information for an IPaddress. If the routing information is not in the local cache, then theborder router 630 may query the mapping service.

Routing Service Optimizations

Some embodiments of a routing service and/or mapping service asdescribed herein may use various business and/or technical data sourcesand policies in making routing decisions to bias traffic distributionbeyond what is normally possible in conventional systems using standardrouting protocol (e.g., BGP) attributes and routing policies. Forexample, one or more of usage data for individual IP address prefixes,Simple Network Management Protocol (SNMP) data from individual links inthe network, Internet “weather” metrics, carrier preferences, and costoptimization metrics may be used in various embodiments, along withappropriate policies, to make routing decisions.

For example, conventional routers are not aware of business logic. Insome embodiments, when evaluating routes in the Internet routing table,the routing service may consider business logic in the decision-makingprocess. As an example, transit providers are generally commercialenterprises that charge fees for routing packets. The routing servicemay thus consider cost when selecting a route; a longer route via firsttransit provider may be selected over a shorter route via a secondtransit provider if the cost of the route via the first provider isless.

As another example, some embodiments may monitor how much traffic iscoming from and/or going to particular destinations on the network. Forexample, a network that provides VMs to customers via hardwarevirtualization technology may monitor traffic to and from individualVMs. Routing decisions for the VMs may be biased by the routing servicebased on volume. Another example use case directed to business logic isto manage total traffic to transit providers. This traffic may be acrossmultiple links in multiple locations. Transit billing arrangements mayinclude minimum commitments that are to be met and that may be measuredmonthly or annually, and traffic may need to be rebalanced to meet thesebusiness goals.

As yet another example, some embodiments may monitor Internet “weather”metrics to determine performance of various routes. If a route (orroutes) with poor performance is detected, the routing service maydirect traffic onto different routes. Some embodiments may send testpackets on various routes, or use some other type of active probing, tomeasure latency or other metrics on various routes, and use thestatistics resulting from this testing to influence routing decisions.

In some embodiments, Simple Network Management Protocol (SNMP) data fromthe network, or some other network protocol, may be used to querydevices in the internal network to monitor, for example, networkcongestion in portions of the internal network (e.g., in various datacenters of the network). If a data center is detected that is havingproblems, e.g. traffic congestion, the routing service and mappingservice may route some network traffic to a different data center on thenetwork before the packets are sent to the Internet.

BGP Peering Alternatives

The above describes a method for using IP tunneling technology toestablish an eBGP peer session between a transit provider and therouting service. Embodiments do not change the standard Internet routingprotocol (e.g., BGP). Normal BGP sessions with transit providers areestablished; however, in embodiments, the sessions terminate at therouting service rather than directly on the border router(s). BGPsupports a standard option for eBGP multi-hop links. Some transitproviders may support this option. Thus, in some embodiments, the borderrouter(s) may be configured to implement this multi-hop option to carrythe eBGP session through to the routing service. For connections totransit services that do not support this option, an IP tunnelingtechnique as described herein may be used to carry the eBGP session tothe routing service.

In some embodiments, for at least some border routers, a TransmissionControl Protocol (TCP) pass-through proxy may be configured on theborder router to carry the eBGP session to the routing service, ratherthan using the eBGP multi-hop option or an IP tunneling technique. TheTCP proxy on a network border router establishes a connection to therouting service, and forwards routing protocol (e.g., BGP) messagesreceived from a respective transit provider network to the routingservice via the connection. The TCP proxy is effectively a small daemonrunning on the network border router. The daemon listens on the TCPport(s) that belong to the routing protocol (e.g., BGP). The daemonestablishes another connection to the routing service. This connectionacts as a pass-through tunnel to the routing service for the routingprotocol messages received from the respective transit provider network.The daemon encapsulates the packets at the application layer of thenetwork rather than at the network layer as is done in the IP tunnelingtechnique. A TCP pass through proxy may allow, for example, thereplication of the routing service to provide redundancy. The routingdaemon can open two (or more) backend connection to two (or more)instances of the routing service and duplicate the routing protocolmessages to the two (or more) instances.

FIG. 9 illustrates establishing a routing protocol peering between atransit provider and a routing service using a TCP proxy, according toat least some embodiments. As indicated at 900, a routing protocol(e.g., BGP) session is established between a small-scale border routeron the network and a transit provider router. BGP (Border GatewayProtocol) is implemented on top of TCP (Transmission Control Protocol);to establish a BGP session, a TCP connection is first establishedbetween the network border router and the transit provider router. Asindicated at 902, routing messages are sent from the transit provider tothe network border router via the routing protocol session. As indicatedat 904, a TCP proxy on the border router forwards the routing messagesto the routing service via a connection to the routing service at theapplication layer of the network. As indicated at 906, the routingservice processes the routing information in the routing messages. Atleast some of the routing information is stored to an Internet routingtable maintained by the routing service.

Redundancy

In some embodiments, redundancy may be provided for some components of anetwork as illustrated in FIGS. 3 and 6. For the routing service, anumber of active/passive and active/active backup mechanisms arepossible to provide redundancy. In some embodiments, upstream updatesmay be replicated. In some embodiments, downstream sessions may bemultiple if necessary or desired. In some embodiments, the routingservice itself may be replicated to provide redundancy. In theseembodiments, for example, a TCP proxy may be implemented on each networkborder router that establishes pass-through connections from arespective network service provider to each instance of the routingservice.

In at least some embodiments, the mapping service may be implemented asa distributed cache of mappings. If the central mapping service fails,the cache persists and traffic continues to flow, although updatescease.

Some embodiments may utilize a multi-path or Equal-Cost Multi-Path(ECMP) strategy to establish more than one best path or route to adestination address in parallel, thus providing route redundancy. ECMPis a routing strategy where packet forwarding to a destination may beperformed over multiple best paths. For example, in some embodiments,the mapping service and routing service may provide routing informationindicating multiple best paths to a destination address, and the networkmay route the packet(s) to the destination over at least two of theindicated paths.

Illustrative System

In at least some embodiments, a server that implements a portion or allof one or more of the technologies, including but not limited to therouting service technology, the mapping service technology, and thesmall-scale border router technology as described herein may include ageneral-purpose computer system that includes or is configured to accessone or more computer-accessible media, such as computer system 1000illustrated in FIG. 10. In the illustrated embodiment, computer system1000 includes one or more processors 1010 coupled to a system memory1020 via an input/output (I/O) interface 1030. Computer system 1000further includes a network interface 1040 coupled to I/O interface 1030.

In various embodiments, computer system 1000 may be a uniprocessorsystem including one processor 1010, or a multiprocessor systemincluding several processors 1010 (e.g., two, four, eight, or anothersuitable number). Processors 1010 may be any suitable processors capableof executing instructions. For example, in various embodiments,processors 1010 may be general-purpose or embedded processorsimplementing any of a variety of instruction set architectures (ISAs),such as the x86, PowerPC, SPARC, or MIPS ISAs, or any other suitableISA. In multiprocessor systems, each of processors 1010 may commonly,but not necessarily, implement the same ISA.

System memory 1020 may be configured to store instructions and dataaccessible by processor(s) 1010. In various embodiments, system memory1020 may be implemented using any suitable memory technology, such asstatic random access memory (SRAM), synchronous dynamic RAM (SDRAM),nonvolatile/Flash-type memory, or any other type of memory. In theillustrated embodiment, program instructions and data implementing oneor more desired functions, such as those methods and techniquesdescribed above for a mapping service, a routing service, small-scaleborder routers, IP tunneling, and/or a VMM hosting multiple VMs on ahost machine, are shown stored within system memory 1020 as code 1025.

In one embodiment, I/O interface 1030 may be configured to coordinateI/O traffic between processor 1010, system memory 1020, and anyperipheral devices in the device, including network interface 1040 orother peripheral interfaces. In some embodiments, I/O interface 1030 mayperform any necessary protocol, timing or other data transformations toconvert data signals from one component (e.g., system memory 1020) intoa format suitable for use by another component (e.g., processor 1010).In some embodiments, I/O interface 1030 may include support for devicesattached through various types of peripheral buses, such as a variant ofthe Peripheral Component Interconnect (PCI) bus standard or theUniversal Serial Bus (USB) standard, for example. In some embodiments,the function of I/O interface 1030 may be split into two or moreseparate components, such as a north bridge and a south bridge, forexample. Also, in some embodiments some or all of the functionality ofI/O interface 1030, such as an interface to system memory 1020, may beincorporated directly into processor 1010.

Network interface 1040 may be configured to allow data to be exchangedbetween computer system 1000 and other devices 1060 attached to anetwork or networks 1050, such as other computer systems or devices asillustrated in FIGS. 3 and 6, for example. In various embodiments,network interface 1040 may support communication via any suitable wiredor wireless general data networks, such as types of Ethernet network,for example. Additionally, network interface 1040 may supportcommunication via telecommunications/telephony networks such as analogvoice networks or digital fiber communications networks, via storagearea networks such as Fibre Channel SANs, or via any other suitable typeof network and/or protocol.

In some embodiments, system memory 1020 may be one embodiment of acomputer-accessible medium configured to store program instructions anddata as described above for FIGS. 3 through 9 for implementingembodiments of methods and apparatus for achieving Internet-scalerouting using small-scale routers and an overlay network. However, inother embodiments, program instructions and/or data may be received,sent or stored upon different types of computer-accessible media.Generally speaking, a computer-accessible medium may include storagemedia or memory media such as magnetic or optical media, e.g., disk orDVD/CD coupled to computer system 1000 via I/O interface 1030. Acomputer-accessible medium may also include any volatile or non-volatilemedia such as RAM (e.g. SDRAM, DDR SDRAM, RDRAM, SRAM, etc.), ROM, etc,that may be included in some embodiments of computer system 1000 assystem memory 1020 or another type of memory. Further, acomputer-accessible medium may include transmission media or signalssuch as electrical, electromagnetic, or digital signals, conveyed via acommunication medium such as a network and/or a wireless link, such asmay be implemented via network interface 1040.

CONCLUSION

Various embodiments may further include receiving, sending or storinginstructions and/or data implemented in accordance with the foregoingdescription upon a computer-accessible medium. Generally speaking, acomputer-accessible medium may include storage media or memory mediasuch as magnetic or optical media, e.g., disk or DVD/CD-ROM, volatile ornon-volatile media such as RAM (e.g. SDRAM, DDR, RDRAM, SRAM, etc.),ROM, etc, as well as transmission media or signals such as electrical,electromagnetic, or digital signals, conveyed via a communication mediumsuch as network and/or a wireless link.

The various methods as illustrated in the Figures and described hereinrepresent exemplary embodiments of methods. The methods may beimplemented in software, hardware, or a combination thereof. The orderof method may be changed, and various elements may be added, reordered,combined, omitted, modified, etc.

Various modifications and changes may be made as would be obvious to aperson skilled in the art having the benefit of this disclosure. It isintended to embrace all such modifications and changes and, accordingly,the above description to be regarded in an illustrative rather than arestrictive sense.

What is claimed is:
 1. A system, comprising: one or more server devicesconfigured to implement a routing service, wherein the routing serviceis an authoritative router for routing packets on a network; one or moreendpoint devices configured to originate packets within the network fordelivery outside the network; and one or more network devices configuredto implement one or more network border routers, wherein each of the oneor more network border routers is connected to a border router of atleast one of one or more transit provider networks, wherein a transitprovider network provides connectivity among networks on an Internet,and wherein at least one of the one or more network border routers isconnected to a given one of the one or more transit provider networks;wherein the routing service is configured to: establish at least oneseparate routing protocol session with each of the one or more transitprovider networks via the one or more network border routers, whereineach routing protocol session is established between the routing serviceon the one or more server devices and a border router of one of the oneor more transit provider networks via one of the one or more networkborder routers of the network connected to the respective one of the oneor more transit provider networks; receive routing information from eachof the one or more transit provider networks via the at least oneseparate routing protocol session with each of the one or more transitprovider networks; store the received routing information as an Internetrouting table on the one or more server devices; and direct routing ofoutgoing packets originating within the network from the one or moreendpoint devices onto the Internet via the one or more network borderrouters according to the routing information in the Internet routingtable stored on the one or more server devices.
 2. The system as recitedin claim 1, wherein each of the one or more network border routers isconnected to a border router of a respective one of the one or moretransit provider networks via a direct physical communications link. 3.The system as recited in claim 1, wherein the one or more network borderrouters are small-scale routers each configured with a capacity tolocally store only a portion of the Internet routing table.
 4. Thesystem as recited in claim 1, wherein the routing protocol is BorderGateway Protocol (BGP).
 5. The system as recited in claim 1, wherein, toestablish a routing protocol session with one of the one or more transitprovider networks via a respective network border router, the routingservice is configured to establish a tunnel over the network between therouting service and the respective network border router according to anInternet Protocol (IP) tunneling technology, wherein the respectivenetwork border router is configured to encapsulate routing protocolmessages received from the transit provider network according to an IPtunneling encapsulation format and forward the encapsulated routingprotocol messages to the routing service via the tunnel.
 6. The systemas recited in claim 1, wherein, to establish a routing protocol sessionwith one of the one or more transit provider networks via a respectivenetwork border router, a Transmission Control Protocol (TCP) proxy isimplemented on the respective network border router, wherein the TCPproxy establishes a connection to the routing service, and wherein theTCP proxy is configured to forward routing protocol messages, receivedfrom the transit provider network, to the routing service via theconnection.
 7. The system as recited in claim 1, further comprising oneor more devices configured to implement a mapping service, wherein, toroute an outgoing packet from an endpoint device onto the Internet viaone of the one or more network border routers according to the routinginformation in the Internet routing table stored on the one or moreserver devices, the mapping service is configured to: receive a queryfrom the endpoint device, wherein the query specifies a destinationInternet IP address for the packet; obtain an indication of a route forthe packet from the routing service according to the destinationInternet IP address; and send an indication of the network border routerthat serves the indicated route to the endpoint device; wherein theendpoint device is configured to send the packet to the indicatednetwork border router via the network; and wherein the network borderrouter is configured to send the packet to the respective transitprovider network.
 8. The system as recited in claim 7, wherein theendpoint device is a virtual machine monitor (VMM) on a host device thatimplements the VMM and one or more virtual machines (VMs), and whereinthe packet originates from one of the VMs on the host device.
 9. Thesystem as recited in claim 7, wherein the network is configured toimplement an overlay network according to Internet Protocol (IP)tunneling technology, wherein, to send the packet to the indicatednetwork border router via the network, the endpoint device is configuredto: encapsulate the packet according to an IP tunneling encapsulationprotocol; and send the encapsulated packet to the network border routervia a tunnel on the overlay network; wherein the network border routeris configured to remove the encapsulation from the packet prior tosending the packet to the respective transit provider network.
 10. Thesystem as recited in claim 1, further comprising one or more devicesconfigured to implement a mapping service configured to obtain routinginformation from the routing service, wherein the network is furtherconfigured to implement an overlay network according to InternetProtocol (IP) tunneling technology; wherein each network border routeris configured to: receive an incoming packet from a respective transitprovider network; query the mapping service with a destination IPaddress on the network indicated by the packet; receive an indication ofan endpoint device on the network that serves the destination IP addressfrom the mapping service; encapsulate the packet according to an IPtunneling encapsulation protocol; and send the encapsulated packet tothe endpoint device that serves the destination IP address via a tunnelon the overlay network; wherein the endpoint device is configured toremove the encapsulation from the packet and forward the packet to thedestination IP address.
 11. The system as recited in claim 10, whereinthe endpoint device is a virtual machine monitor (VMM) on a host devicethat implements the VMM and one or more virtual machines (VMs), andwherein the destination IP address is one of the VMs on the host device.12. The system as recited in claim 1, further comprising one or moredevices configured to implement a mapping service configured to obtainrouting information from the routing service, wherein at least one ofthe one or more network border routers is configured to: maintain alocal cache of routing information; receive incoming packets from atleast one of the one or more transit provider networks; for eachreceived incoming packet: check the local cache of routing informationto determine if there is cached routing information for a destinationaddress on the network indicated by the packet; if there is cachedrouting information for the destination address in the local cache,route the packet to the destination address on the network according tothe cached routing information for the destination address; and if thereis no cached routing information for the destination address in thelocal cache, query the mapping service with the destination address onthe network indicated by the packet to obtain routing information forthe destination address.
 13. A method, comprising: establishing, by arouting service implemented on one or more server devices on a network,at least one separate routing protocol session with each of one or moretransit provider networks, wherein the routing service is anauthoritative router for routing packets on the network, wherein atransit provider network provides connectivity among networks on anInternet, and wherein each routing protocol session is established bythe routing service on the one or more server devices to a border routerof one of the one or more transit provider networks via one of one ormore network border routers of the network connected to the respectiveone of the one or more transit provider networks; receiving, by therouting service, routing information from each of the one or moretransit provider networks via the at least one separate routing protocolsession with each of the one or more transit provider networks; storingthe received routing information as an Internet routing table on the oneor more server devices; and directing, by the routing service, routingof outgoing packets originating within the network from one or moreendpoint devices on the network onto the Internet via the one or morenetwork border routers according to the routing information in theInternet routing table stored on the one or more server devices.
 14. Themethod as recited in claim 13, wherein the one or more network borderrouters are small-scale routers each configured with a capacity tolocally store only a portion of the Internet routing table.
 15. Themethod as recited in claim 13, wherein the routing protocol is BorderGateway Protocol (BGP).
 16. The method as recited in claim 13, whereinsaid establishing at least one separate routing protocol session witheach of one or more transit provider networks comprises: establishing,for each routing protocol session, a separate tunnel over the networkbetween the routing service and each network border router according toan Internet Protocol (IP) tunneling technology; and encapsulating, byeach network border router, routing protocol messages received from arespective transit provider network according to an IP tunnelingencapsulation format and forwarding the encapsulated routing protocolmessages to the routing service via the respective tunnel.
 17. Themethod as recited in claim 13, wherein said routing of outgoing packetsfrom endpoint devices on the network onto the Internet via the one ormore network border routers according to the routing information in theInternet routing table stored on the one or more server devicescomprises: an endpoint device on the network obtaining, from the routingservice, an indication of a network border router that serves a selectedroute for a packet; the endpoint device sending the packet to theindicated network border router via the network; and the network borderrouter sending the packet to a respective transit provider network thatprovides the selected route.
 18. The method as recited in claim 17,wherein the network implements an overlay network according to InternetProtocol (IP) tunneling technology, wherein said sending the packet tothe indicated network border router via the network comprises:encapsulating the packet according to an IP tunneling encapsulationprotocol; and sending the encapsulated packet to the network borderrouter via a tunnel on the overlay network; wherein the network borderrouter is configured to remove the encapsulation from the packet priorto said sending the packet to the respective transit provider network.19. The method as recited in claim 13, wherein the network implements anoverlay network according to Internet Protocol (IP) tunnelingtechnology, the method further comprising: receiving, by a networkborder router on the network, an incoming packet from a respectivetransit provider network; querying, by the network border router, amapping service with a destination IP address on the network indicatedby the packet, wherein the mapping service is configured to obtainrouting information from the routing service; receiving, by the networkborder router, an indication of an endpoint device on the network thatserves the destination IP address from the mapping service;encapsulating, by the network border router, the packet according to anIP tunneling encapsulation protocol; sending, by the network borderrouter, the encapsulated packet to the endpoint device that serves thedestination IP address via a tunnel on the overlay network; andremoving, by the endpoint device, the encapsulation from the packet andforwarding the packet to the destination IP address.
 20. Anon-transitory computer-accessible storage medium, storing programinstructions, which, when executed by one or more service devices on anetwork, cause the one or more service devices to: establish, by arouting service, at least one separate routing protocol session witheach of one or more transit provider networks, wherein the routingservice is an authoritative router for routing packets on the network,wherein a transit provider network provides connectivity among networkson an Internet, and wherein each routing protocol session is establishedby the routing service on the one or more server devices to a borderrouter of one of the one or more transit provider networks via one ofone or more network border routers of the network connected to therespective one of the one or more transit provider networks; receiverouting information from each of the one or more transit providernetworks via the at least one separate routing protocol session witheach of the transit provider networks; store the received routinginformation as an Internet routing table on the one or more serverdevices; and direct routing of outgoing packets originating within thenetwork from one or more endpoint devices on the network onto theInternet via the one or more network border routers according to therouting information in the Internet routing table stored on the one ormore server devices; wherein said routing of at least one of the one ormore outgoing packets is performed according to the routing informationin the Internet routing table stored on the one or more server deviceswithout accessing routing information stored on the one or more networkborder routers.
 21. The non-transitory computer-accessible storagemedium as recited in claim 20, wherein the one or more network borderrouters are small-scale routers each configured with a capacity tolocally store only a portion of the Internet routing table.
 22. Thenon-transitory computer-accessible storage medium as recited in claim20, wherein the routing protocol is Border Gateway Protocol (BGP). 23.The non-transitory computer-accessible storage medium as recited inclaim 20, wherein, to establish at least one separate routing protocolsession with each of one or more transit provider networks, the routingservice is operable to: establish, for each routing protocol session, aseparate tunnel over the network between the routing service and arespective network border router according to an Internet Protocol (IP)tunneling technology; wherein the routing service is operable to receiveencapsulated routing protocol messages from the one more transitprovider networks via the tunnels, wherein the routing protocol messagesare encapsulated according to an IP tunneling encapsulation format andforwarded to the routing service via the tunnels at the network borderrouters.
 24. The non-transitory computer-accessible storage medium asrecited in claim 20, wherein, to establish at least one separate routingprotocol session with each of one or more transit provider networks, therouting service is operable to establish the routing protocol sessionsvia a connection to a Transmission Control Protocol (TCP) proxy on eachnetwork border router, wherein each TCP proxy is configured to forwardrouting protocol messages, received from the respective transit providernetwork, to the routing service via the connection.
 25. Thenon-transitory computer-accessible storage medium as recited in claim20, wherein, to direct routing of outgoing packets from one or moreendpoint devices on the network onto the Internet via the one or morenetwork border routers according to the routing information in theInternet routing table stored on the one or more server devices, therouting service is operable to: receive a query for routing informationfor a packet from an endpoint device; and send an indication of anetwork border router that serves a selected route for the packet to theendpoint device; wherein the endpoint device is configured to send thepacket to the indicated network border router via the network, andwherein the network border router is configured to send the packet to arespective transit provider network that provides the selected route.26. The non-transitory computer-accessible storage medium as recited inclaim 25, wherein the network implements an overlay network according toInternet Protocol (IP) tunneling technology, wherein, to send the packetto the indicated network border router Via the network, the endpointdevice is configured to: encapsulate the packet according to an IPtunneling encapsulation protocol; and send the encapsulated packet tothe network border router via a tunnel on the overlay network; whereinthe network border router is configured to remove the encapsulation fromthe packet prior to said sending the packet to the respective transitprovider network that provides the selected route.
 27. Thenon-transitory computer-accessible storage medium as recited in claim20, wherein routing service is further operable to direct routing ofincoming packets from the one or more network border routers todestination IP addresses on the network according to the routinginformation in the Internet routing table stored on the one or moreserver devices.
 28. A server system, comprising: at least one processor;a network interface configured to couple to a network; and a memorycomprising program instructions, wherein the program instructions areexecutable by the processor to: establish, by an authoritative routingservice for the network, at least one separate routing protocol sessionwith each of one or more transit provider networks via one or morenetwork border routers on the network, wherein a transit providernetwork provides connectivity among networks on an Internet, and whereinat least one of the one or more network border routers is connected to agiven one of the one or more transit provider networks, wherein eachrouting protocol session is established between the routing service anda border router of one of the one or more transit provider networks viaone of the one or more network border routers of the network connectedto the respective one of the one or more transit provider networks;receive routing information from each of the one or more transitprovider networks via the at least one separate routing protocol sessionwith each of the one or more transit provider networks; store thereceived routing information as an Internet routing table on the serversystem; and direct routing of outgoing packets originating within thenetwork from one or more endpoint devices on the network onto theInternet via the one or more network border routers according to therouting information in the Internet routing table.
 29. The server systemas recited in claim 28, wherein the one or more network border routersare small-scale routers each configured with a capacity to locally storeonly a portion of the Internet routing table.
 30. The server system asrecited in claim 28, wherein the routing protocol is Border GatewayProtocol (BGP).